Add speculative support for OpenBSD.

[grynspan]

OpenBSD has partial support in the Swift toolchain. This PR adds speculative support for it based on the assumption that what works with FreeBSD will generally also work with OpenBSD. The big differences:

1. We need to include <util.h> instead of <libutil.h>,
2. /usr/bin/tar does not support writing PKZIP files (so we look for the optional /usr/bin/zip instead), and
3. OpenBSD has no way to determine the path to the current executable, so we naïvely assume argv[0] is correct.

These changes are speculative and have not been tested.

Partially resolves #888.

Checklist:

• Code and documentation should follow the style of the Style Guide.
• If public symbols are renamed or modified, DocC references should be updated.

[grynspan]

@swift-ci test

[grynspan]

@swift-ci test

[michael-yuji]

For (2) I know at least for FreeBSD there’s no /usr/bin/zip, I’m not sure about OpenBSD

For (3) I think we get get it via sysctl
cc @3405691582 who have been working on OpenBSD support

Edit(3): found it https://github.com/swiftlang/swift-corelibs-foundation/blob/25d044f2c4ceb635d9f714f588673fd7a29790c1/Sources/CoreFoundation/CFPlatform.c#L224

[grynspan]

Yeah that's just argv[0] again, unfortunately!

[grynspan]

For (2) I know at least for FreeBSD there’s no /usr/bin/zip, I’m not sure about OpenBSD

Fortunately, for FreeBSD we can and do just use libarchive via /usr/bin/tar. On OpenBSD, from what I can gather /usr/bin/zip exists as an optional package, but is not installed by default.

[michael-yuji]

re: zip, I think for installed packages, it should be in /usr/local prefix on OpenBSD?

[grynspan]

If I could get a VM set up, I'd check!

[3405691582]

Zip is in an optional package; these binaries go in /usr/local.

$ doas pkg_add zip
quirks-7.79 signed on 2025-01-02T10:42:16Z
zip-3.0p3: ok
$ which zip
/usr/local/bin/zip

[3405691582]

Other than the zip path, the changes look reasonable; I haven't been able to locally test fully due to the fact that bootstrapping a fully-featured toolchain is incomplete (see swiftlang/swift#78437), but I can revisit once I have a proper toolchain.

[grynspan]

If you want to give the PR a ✅, we can merge it (with the path fix, of course.) Or if you'd prefer to wait until you have an otherwise-functional toolchain, I can close this PR for now.

[grynspan]

@swift-ci test

[3405691582]

I'm happy if you merge sooner rather than later, and we take care of any missing pieces then.

[grynspan]

Sounds good to me. Will chat with my colleagues today about it, should be able to merge before EOD.